Directional couplers are commonly used for isolating, separating or combining signals. A typical directional coupler includes a coupling line (or auxiliary arm) that is positioned in proximity to a main line (or transmission line), with the coupling and main lines being electrically isolated from each other across an intervening non-conductive medium (e.g., air and/or a dielectric material). When a forward wave is provided in the main line (e.g., a wave having a direction of propagation from an input port toward an output port of the main line), an induced wave is produced in the coupling line. The magnitude of the induced wave is proportional to the magnitude of the forward wave, and the ratio of the induced power to the input power is referred to as the “coupling factor.” The “directivity” of a particular directional coupler is the difference (e.g., in decibels (dB)) of the power output at a coupled port, when power is transmitted in the desired direction, to power output at the same coupled port when the same amount of power is transmitted in the opposite direction.